Abstract:
Traditional censorship revolves around blocking access to some websites (or services) over the Internet. However, recently there has been a rise in the events of an extreme form of censorship viz., deliberate Internet shutdown, leading to complete Internet disconnection, severely impacting lives in such regions. Naturally, these shutdowns render all existing circumvention schemes unusable. Thus, we present Dolphin, a first of its kind system that can provide access to lightweight and delay tolerant Internet applications (email, tweets, news snippets, etc.) during Internet shutdowns. Dolphin uses the cellular voice channel to transmit data bits. A user in the shutdown region (who wishes to access these applications) requires a peer in non-shutdown region to send and retrieve content on its behalf. The data bits between the peers are sent by first encoding them into audio and then transmitting them over a cellular voice call. We overcome multiple challenges while designing and implementing Dolphin. E.g., the cellular voice channel is inherently lossy and unreliable. But the Internet applications need reliable transfers. Thus, in Dolphin we develop a TCP-style reliability layer to overcome the losses that works atop any underlying encoding and modulation scheme. Further, to evade eavesdroppers over the insecure voice channel, we provide end-to-end confidentiality. Also, Dolphin can function even without human intervention, by using cellular voice automation services. We experimentally show that Dolphin works for Internet applications, by testing it for sending email, tweets and accessing news snippets. All these applications take a few minutes to be accessed (e.g., a 500 character email was received in under 2 minutes).
